The present disclosure relates generally to variable amplitude controllers, such as variable gain amplifiers and variable attenuators. More particularly, the present application relates to a variable amplitude controller having a high degree of gain variation with minimal insertion phase modulation.
Variable amplitude controllers are used in a variety of applications ranging from speaker systems to wireless communication systems. In radio and other high-frequency applications, amplitude controllers are used to control the amplitude of a transmitted or received signal. In many of these applications, a variable amplitude controller is used to allow variable control over the degree of attenuation or gain provided by the amplitude controller.
Variable amplitude controllers generally fall into two categories: digital amplitude controllers and analog amplitude controllers. A digital amplitude controller operates in a step-like manner and allows for the amount of gain or attenuation to be controlled subject to minimum attenuation or gain step. Such a digital amplitude controller may receive n-number of bits to control the amount of gain or attenuation applied to an input signal. Each bit ranging from the least-significant bit (LSB) of the control signal to the most-significant bit (MSB) of the control signal may apply a greater amount of attenuation or gain to the input signal. For example, the smallest amount of attenuation or gain that a particular digital amplitude controller may apply is −0.5 decibels (dB) of attenuation from the LSB, followed by 1 dB of attenuation for the next bit, followed by 2 dB of attenuation for the bit after that, etc. A variable analog amplitude controller, in contrast, offers the potential for a continuous range of control over the attenuation or gain applied to a signal. However, all devices that adjust the amplitude of a signal will also apply a certain amount of insertion phase shift to the amplitude-adjusted signal by virtue of their operation, due to non-ideal circuit realities such as imperfect circuit element interaction with parasitic stray capacitance across the amplitude control range. Accordingly, applicants have discovered that there may be a need for an analog amplitude controller that exhibits a minimal phase shift while supporting a wide range of amplitude control.